In the case of an acute stroke in the brain of a patient, the reduction of blood supply causes a part of the brain tissue to suffer from ischemia, i.e., suffer from inadequate oxygen and nutrient supply, which part is known as the perfusion lesion. A sub-part of the perfusion lesion may be irreversibly damaged, which part is known as the core lesion or diffusion lesion. The remaining part of the perfusion lesion, the so-called ischemic penumbra, may be salvaged if blood supply is restored within a short time-frame, such as within a few hours. Identification of the volume and location of the penumbra is critical in deciding therapeutic strategy for individual stroke patients. Since therapy, such as therapy with thrombolytic agents, must be initiated within a short time frame, rapid assessment is pivotal.
The size and location of the core and perfusion lesions is typically determined by manual inspection of diffusion weighted and perfusion weighted magnetic resonance imaging (DWI/PWI) modalities. This requires intervention by highly skilled experts, such as stroke neuroradiologists. Such manual determination of DWI/PWI mismatch can be time consuming and costly.
WO2007/058632A1 describes that brain images are processed and analyzed with the aid of a computer for stroke diagnosis or therapeutic decision making, where multiple stroke-related images are superimposed.
Such automated image processing methods may not be reliable since they may not be able to distinguish between a lesion volume and a volume outside of the lesion.
Simple thresholding has been attempted in order to automatically define hypoperfused tissue. This approach, however, suffers from the lack of established thresholds, such as perfusion thresholds, applicable across individuals. Furthermore, studies have shown that thresholds depend on numerous factors including time from symptom onset and post-processing methodology.
Hence, an improved method for computer assisted delineation of tissue lesions would be advantageous, and in particular a method being faster and/or more reliable would be advantageous.